In typical cellular applications, an active subscriber identity needs to be registered in a corresponding network to be able to perform communication via the network. Such communication may, for example, comprise initiate and receive calls, SMS (short message service) and the like. Thus, an aim of performing a registering procedure towards a network is to inform the network that the mobile terminal associated with the subscriber identity is switched on and is able to receive paging and other messages from the network.
When a subscriber identity performs a de-registration from a network, a purpose is to inform the network that the mobile terminal associated with the subscriber identity is switched off and, hence, that paging and other messages should not be broadcasted anymore.
A registered subscriber identity may also perform update procedures towards the network at defined moments in time.
This may for example be the case when the location of the mobile terminal has changed.
Another example is that a typical network may require a registered subscriber identity to perform a periodic update procedure towards the network to confirm its active status (and possibly its location).
Typically, the network maintains a timer for this purpose. The timer is reset whenever a subscriber identity performs a registration or update procedure. If the timer expires, the network typically considers the subscriber identity as de-registered. This has the advantage that the network will not waste efforts in trying to reach a subscriber identity that has become un-reachable without having performed the de-registration procedure (e.g. due to loss of coverage, low battery, battery removal, etc.). A typical timer setting may be that it expires after approximately 6 hours or more than 6 hours. The example timer T3212 in 3GPP specification TS24.008 has an expiry setting of 6 hours.
A corresponding timer (typically shorter than the network timer) is maintained in the mobile terminal for the subscriber identity. This timer is also reset whenever a subscriber identity performs a registration or update procedure. When the timer expires, a periodic update procedure for the subscriber identity should typically be initiated by the mobile terminal. Examples of such timers are the timers T3212 and T3312 in 3GPP specification TS24.008. The timer duration value(s) may typically be either strictly defined in an applicable standard or broadcast by the network (e.g. in a System Information signaling). The timer maintained in the mobile terminal for the subscriber identity typically has a timer duration value that is directly related to the timer duration value of the corresponding timer maintained in the network.
Related to a subscriber identity, a corresponding context is maintained in the network for that particular subscriber identity. The context may, among other things, maintain information regarding the status of the subscriber identity (e.g. registered or de-registered) and location information of the subscriber identity (e.g. home location and temporary location, such as local temporary identity—TMSI (temporary mobile subscriber identity)/P-TMSI (packet temporary mobile subscriber identity)). Some information of the context may be always maintained (e.g. status and home location), while other information may only be maintained while the subscriber identity is registered (e.g. temporary location).
The context is updated when a subscriber identity is registered, updated and/or de-registered in the network. The context may also be updated at other times.
Due to this context, the network is able to know if a particular subscriber identity is able to receive messages (e.g. paging) or not, and at which location the network should transmit the messages.
For a single subscriber identity device (e.g. a single SIM phone), the registration procedure is typically performed at power on and the de-registration at power off.
For a dual or multiple subscriber identity device that can only have a limited number of subscriber identities active at each moment in time (e.g. a dual SIM single standby—DSSS—phone), registration/de-registration procedures are typically also performed at a switch of active subscriber identity.
A DSSS phone is equipped with two subscriber identity means (e.g. two SIM sockets and two copies any hardware directly associated with the SIM sockets), but is otherwise similar to a single subscriber identity device (e.g. having single SIM software and hardware architecture). From a user perspective, a DSSS phone provides the possibility to use two different subscriber identities in one single device without having to perform a physical subscriber identity module exchange. However, only one subscriber identity is available at each moment in time for a DSSS phone. When one subscriber identity is activated by the user, the other subscriber identity is in an off state. Thus, the user does not have any access to the other subscriber identity and no communication can be performed for the other subscriber identity.
The behavior towards the network of DSSS is not specified in any standard. Typically, single subscriber identity device behavior is adopted by default. Thus, when a user initiates a switch of active subscriber identity on a DSSS phone, a procedure is performed similar to that of a SIM removal and insertion of another SIM in a single SIM device.
In order to switch from one subscriber identity to another in a DSSS device, a complete re-initialization to the other subscriber identity of the telecom stack of the device is typically needed. Also typically, various switch off/on procedures (including network procedures such as de-register/register and detach/attach for CS (circuit switched) and PS (packet switched) domains) will be performed for the respective subscriber identities to be de-activated and activated respectively.
The registration and de-registration processes takes some time. In an example scenario, the de-registration/registration processes of a subscriber identity switch in a DSSS device typically takes approximately 8 seconds of the totally 15-30 seconds needed for the subscriber identity switch.
If several subscriber identity switches are performed in sequence, there is a risk of signaling overload towards the network. Naturally, a situation of signaling overload should preferably be avoided.
Naturally, the operations performed and the signaling involved in association with registration/de-registration also consumes power.
These problems are experienced for subscriber identity switches in both single and multiple subscriber identity devices. Some problems are typically more pronounced in multiple subscriber identity devices, for example the delay problem (since the delay due to the problems described above comprise a larger portion of the total time required for a subscriber identity switch in a multiple subscriber identity device than in a single subscriber identity device).
Therefore, there is a need for improved methods and arrangements of active subscriber identity switch.